A pick-up truck has a cargo bed used to carry various cargos. Generally, the cargo bed is covered by a tonneau cover which is releasably clamped to and extended above the cargo bed, so as to protect the carried cargos from adverse weather and improve the aesthetic appearance of the pick-up truck. The tonneau covers can be classified into hard-top type and soft-top type, wherein the hard-top type tonneau cover has a hard top made of metal, fiberglass or the like, while the soft-top type tonneau cover has a soft top made of canvas, vinyl plastic or a weather-resistant fabric.
In general, although the hard-top tonneau cover provides greater security for cargo and can be more easily clamped on the cargo bed of the pick-up truck, it is heavier than the soft-top tonneau cover, and it needs more storage space for storing the hard-top tonneau cover after being removed from the pick-up truck. Furthermore, the soft-top tonneau cover is lighter in weight, and the volume thereof is more compact for storage. Meanwhile, both of the hard-top tonneau cover and the soft-top tonneau cover need to provide clamps for securely clamping the tonneau cover to the pick-up truck.
For example, U.S. Pat. No. 7,334,830 discloses a tonneau cover for the bed of a pick up truck, which comprises: three sections, each of which includes a frame having two side rails joined by two support rails; a flexible cover overlaying and connected to each of the sections, wherein the side rails of the three sections are hinged together, so as to allow one of the sections to fold onto another adjacent section; and at least one clamp is mounted to the frame of one of the sections, wherein the clamp is used to releasably secure the sections to the pick up truck. The clamp includes: a base portion fixed with respect to the frame of one of the sections; an arm connected to the base; a truck grip member movably mounted on the arm; and a cam lock adjustably mounted on the arm and movably engaging the truck grip member, wherein the base portion is integrated into one of said support rails and the base portion includes a slotted track for receiving the arm, the arm is formed as a threaded post mounted within the slotted track and movable along the track, the truck grip member includes an engaging portion for engaging a surface of a bed wall of the pick up truck.
However, in the '830 patent, the truck grip member and the cam lock are moved along the slotted track by the arm, but the sliding movement of the arm in relation to the slotted track is generally unstable and not smooth due to a single support point of the threaded post of the arm in the slotted track. Further, the threaded post of the arm must strongly abut against an inner edge of the slotted track of the base portion when the engaging portion of the truck grip member is engaged with the bed wall of the pick up truck. After long-term use, the inner edge of the slotted track of the base portion may deform outwardly by the abutment of the threaded post of the arm, so as to increase the distance between the engaging portion of the truck grip member and the bed wall of the pick up truck, resulting in a loose clamping relationship therebetween. In addition, the threaded post of the arm also may deform due to abutting against the inner edge of the slotted track. If the width of the deformed threaded post is smaller than the width of the slotted track, the deformed threaded post of the arm may depart from the slotted track of the base portion, resulting in the structural damage of the clamp.
Moreover, U.S. Pat. No. 7,258,387 discloses a similar clamp for securing a tonneau cover to the rail of a truck bed sidewall, the clamp comprises: a base adapted for securing the cover to the truck bed sidewall; a handle connected at one end by an elongated fastener to the base; a cam part located between the base and the handle, wherein the handle includes a beveled cam surface, the cam part includes a follower in contact with the cam surface. Therefore, the cam part can shift toward and away from the base as the follower is moved along the cam surface when the handle is rotated about a longitudinal axis of the fastener between an open position and a closed position of the cover. The cam part includes an engagement part for making clamping contact with the truck bed sidewall when the handle is in its closed position.
Similarly, in the '387 patent, because the cam part and the handle are moved along a slot of the base by the fastener, but the sliding movement of the fastener in relation to the slot is generally unstable and not smooth due to a single support point of an inner end of the fastener in the slot. Further, the inner end of the fastener must strongly abut against an inner edge of the slot of the base when the engagement part of the cam part is engaged with the bed wall of the pick up truck. After long-term use, the inner edge of the slot of the base may deform outwardly by the abutment of the inner end of the fastener, so as to increase the distance between the engagement part of the cam part and the bed wall of the pick up truck, resulting in a loose clamping relationship therebetween. In addition, the inner end of the fastener also may deform due to abutting against the inner edge of the slot. If the width of the deformed inner end is smaller than the width of the slot, the deformed inner end of the fastener may depart from the slot of the base, resulting in the structural damage of the clamp.
As a result, it is important for related designers and manufacturers to think how to develop a clamp structure for a tonneau cover of a pick-up truck, in order to solve the problems existing in the conventional clamps, as described above.